It is known that corresponding line-bound supply networks are available for transmitting electrical energy. Depending on the electrical power which is to be transmitted, the supply networks have a rated voltage of, for example, 380 kV, 110 kV or else 10 kV, wherein a network frequency of 50 or 60 Hz may be used. A supply network for supplying fixed consumers may be constructed in 3 phases, and therefore a system with three supply lines is available. In the symmetrical state of the lines of this system, the current and voltage are equal in absolute value given a phase shift of 120° in relation to each other in each case.
Energy supply systems for mobile consumers such as, for example, railways or trams may be constructed with a single phase, for example, the supply is provided via an individual supply line, with the feedback then occurring via the metallic rail. In the case of overhead line buses, two supply lines are provided due to the absence of a rail which can be used as a return conductor. The network frequency in such applications is, for example, in Europe, 16 2/3, 25, 50 or 60 Hertz, and in some cases, such as in trams, direct voltage may be occasionally used.
In order to transform the typical alternating supply voltage from 10 kV to 15 KV, mobile transformers are provided which are then integrated, for example, into the underfloor region of a passenger train.
Owing to the underfloor arrangement, the mobile transformers only have a very limited space available, particularly with respect to the height and are usually embodied as oil transformers. On the one hand, the oil serves here as a coolant for conducting away the waste heat which is produced during operation, and as an insulating means, by which small insulating distances, and therefore a compact design, can be implemented.
However, it is disadvantageous for mechanical reasons that such a transformer can usually only be arranged in a stationary fashion, that is to say with a limb axis which is oriented perpendicularly, but this does not correspond to the flat space available in the underfloor region. In addition, for safety reasons, oil, as a combustible medium, is to be avoided in the means of transportation if possible. A lying arrangement uses the space available significantly better but mechanical problems occur with the compressive loading of the winding which is then in a lying position and via which the core weight is transmitted. Embodiment variants with dry transformers are also known, which transformers are, however, also arranged in a standing position due to the problems of compressive loading of the windings, in which case increased cooling also has to be ensured owing to the absence of oil.